A natural grass turf covering has traditionally been cultivated on most playing areas for athletic games. Grass is considered highly desirable both because it stabilizes the soil thereby limiting problems with mud or dust, and also because of its attractive appearance. However, maintainence of natural grass turf on athletic playing areas is very expensive and is practically impossible on areas subjected to continuous heavy usage.
In order to minimize the expense of maintaining athletic playing areas as well as increase the durability of the playing surfaces, attempts have been made to substitute synthetic turf for natural turf. The results of prior efforts have, however, left much to be desired. Particularly severe problems arise in the construction of fields for contact sports such as football, rugby, soccer, field hockey, baseball and the like.
In an effort to achieve some degree of resilience, many prior art synthetic turfs have incorporated an elastomeric foam underlay or backing similar to a carpet pad. Synthetic turfs with foam backing are typlified by the materials in Faria, U.S. Pat. No. 3,332,828 and Spinney, U.S. Pat. No. 3,661,687. Such turfs have an unnatural, springy or spongy feel which reduces the surefootedness of players running and making sharp turns thereon. The surface may be slippery due to graininess or the presence of moisture. Players falling on such surfaces may receive severe rug-burns. The degree to which such surfaces contribute to player injuries has been a matter of substantial controversy.
Top-dressed playing surfaces for athletic games are disclosed in my prior U.S. Pat. Nos. 3,995,079 and 4,044,179. The '079 patent discloses golf greens formed from a turf-like pile fabric top-dressed with non-compacting granular material such as granulated coal slag, crushed flint or crushed granite. Angular top-dressing materials of this type are very abrasive and may scrape the skin of a person falling on the surface. Moreover, such top-dressing materials generally are not readily available in all areas, and consequently, undesirable expense and difficulty may be encountered in installing such surfaces.
U.S. Pat. No. 4,044,179 shows a playing surface comprising a pile fabric with piles resembling grass disposed upon a firm, stable subsurface and top-dressed with sand containing a small amount of moisture modifying material. The sand top-dressing compacts to form a dense, hard layer. This surface is well suited for tennis courts and also can be used for other games. Surfaces of this type are not entirely satisfactory for fields for contact sports because the compaction of the top-dressing limits the shock absorbing ability of the surface and because the sand top-dressing is only slightly less abrasive than non-compacting angular particle dressings.
Playing surfaces have also been constructed with compacted sand top-dressings and resilient underpads as described in co-pending U.S. patent application Ser. No. 115,141 filed Jan. 24, 1980 now abandoned. These surfaces have outstanding shock absorbing character and provide a natural turf-like feel for players walking or running thereon. They are particularly well suited for ball control games such as golf, tennis, lawn bowling, cricket and the like. However, the abrasiviness of the compacted sand top-dressing remains a problem in contact sports where players not infrequently fall or are knocked down on the playing surface. Moreover, the use of a resilient underpad substantially increases the cost of the playing surface and simultaneously decreases the service life of the surface since the underpads deteriorate over time.
There remains a need for a highly durable, less expensive synthetic turf playing surface which closely simulates the appearance and physical character of natural turf without presenting an abrasive surface. There is a particular need for a synthetic turf playing surface which does not give the feeling of running or walking across a springy or spongy surface.